The usual golf ball manufacturing techniques include several different steps, depending on the type of ball, such as one, two, three or even more than three piece balls. According to the traditional method, a solid or composite elastomeric core is made, and an outer dimpled cover is formed around the core.
The two standard methods for molding a cover over a core or a core and inner layers is by compression molding or injection molding. The compression molding operation is accomplished by using a pair of hemispherical molds each of which has an array of protrusions machined or otherwise provided in its cavity, and those protrusions form the dimple pattern on the periphery of the golf ball during the cover molding operation. A pair of hemispherical cover blanks, are placed in a diametrically opposed position on the golf ball body, and the body with the cover blanks thereon are placed in the hemispherical molds, and then subjected to a molding operation. The combination of heat and pressure applied during the molding operation results in the cover blanks being fused to the golf ball body and to each other to form a unitary one-piece cover structure which encapsulates the golf ball body. In addition, the cover blanks are simultaneously molded into conformity with the interior configuration of the hemispherical molds which results in the formation of the dimple pattern on the periphery of the golf ball cover. The drawbacks are that half shells must be molded in advance, the core and shell assemblies must be hand or machine assembled and carefully placed in the mold cavity itself to prevent separation.
In the injection molding of a cover over a core or a core and inner layers retractable pins are usually employed. U.S. Pat. No. 5,147,657 issued Sep. 15, 1992 to Giza discloses a typical retractable pin mold. Retractable pins extend into the mold cavity to support the core as a resinous cover material is injected around the core. The pins, however, must be withdrawn from the heated cover material when it is fluid enough to fill in the pin holes, yet solid enough to support the core. This timing is critical and the process has several drawbacks. The retractable pins are prone to wear and breakage, and are costly to make. The mold itself requires expensive and complicated gates. The timing is difficult to achieve. And, the gating and retractable pins produce numerous surface blemishes on the ball that must be removed in subsequent manufacturing processes.
As in all molding operations, when the golf ball is removed from the hemispherical molds subsequent to the molding operation, it will have molding flash, and possibly other projecting surface imperfections thereon. The molding flash will be located at the fused circular junction of the cover blanks and the parting line of the hemispherical molds. The molding flash will therefore be on a great circle of the spherical golf ball, and that great circle is sometimes referred to in the golf ball art as the “equator” of the golf ball.
The molding flash and possible other projecting surface imperfections, needs to be removed and this is normally accomplished by a grinding, or other trimming operation. Due to the need for grinding, the molding operation must be accomplished in such a manner that the molding flash is located solely on the surface of the golf ball and does not extend into any of the dimples. In other words, a grinding operation may have difficulty reaching into the dimples of the golf ball to remove the molding flash without ruining the golf ball cover.
Therefore, the prior art hemispherical molds are fabricated so that the protrusions formed therein are set back from the circular rims, or mouths of their cavities. The result is that the equator of a molded golf ball is devoid of dimples and the molding flash is located solely on the smooth surface provided at the equator of the golf ball.
In addition to facilitating the grinding-off of molding flash, the protrusions formed in the cavities of the hemispherical molds are set back from the circular mouths of the molds to facilitate removal of the molded golf ball from the mold cavity after completion of the molding operation. If projections were formed at the circular mouths of the molds, they would extend into dimples formed at the equator of the golf ball, and pulling the molded golf ball from the mold cavity in directions perpendicular to the plane of the equator would be difficult, if not impossible.
As is well known, the dimple pattern of a golf ball is a critical factor insofar as the flight characteristics of the ball are concerned. The dimples determine the lift and flight stability of the golf ball. When a golf ball is struck properly, it will spin about a horizontal axis and the air friction and air currents produced by the dimples of the spinning ball will act on the ball and thus determine the lift and flight stability thereof.
In order for a golf ball to achieve optimum flight stability, its dimples must be disposed symmetrically relative to a plane that is perpendicular to its horizontal axis of rotation. Any deviation from such symmetry will result in unequal air friction and air currents acting on the ball thus causing it to deviate from the intended flight path.
In that prior art golf balls are manufactured with a smooth surface along an equator of the ball, the only possible symmetrical arrangement of the dimple patterns that can be provided on these balls is relative to the equator. In other words, the dimple arrays on the hemispherical portions on opposite sides of the equator can be symmetrically arranged with respect to each other. If such symmetry is achieved during manufacturing of a prior art golf ball, the dimple arrays will, of course, be symmetrical relative to the equator. The dimple pattern cannot possibly be symmetrical relative to any other great circle on the spherical surface of the prior art golf balls in that the smooth surface of the equator will interrupt and thus destroy the symmetry.
U.S. Pat. No. 5,798,071 issued to Boehm on Aug. 25, 1998 discloses a process to improve upon the typical injection and compression molding methods. Boehm manufactures a golf ball by injection molding a single piece golf ball preform that replaces the core and two hemispherical shell assemblies. The preform is then compression molded to create the finished golf ball. Using a two mold system, Boehm does not create a cover wherein dimples may be placed upon the equator.
Some U.S. Patents that seek to place dimples upon the equator of the ball include U.S. Pat. Nos. 6,200,232, 6,123,534 and 5,688,193 to Kasashima et al., U.S. Pat. No. 5,840,351 to Inoue et al., and U.S. Pat. No. 4,653,758 to Solheim. All of these patents utilize a two plate mold, and must make provision for the handling of excess flash.
Therefore, a need exists for a new and improved golf ball, with a method and molds for making same, which overcome some of the problems and shortcomings of the prior art.